1. Said when the correct response is too complicated to enunciate,
or the speaker has not thought it out. Often prefaces a longer answer, or
indicates a general reluctance to get into a long discussion. “Don't
you think that we could improve LISP performance by using a hybrid
reference-count transaction garbage collector, if the cache is big enough
and there are some extra cache bits for the microcode to use?”
“Well, mumble ... I'll have to think about it.”

2. [MIT] Expression of not-quite-articulated agreement, often used
as an informal vote of consensus in a meeting: “So, shall we dike out
the COBOL emulation?” “Mumble!”

3. Sometimes used as an expression of disagreement (distinguished
from sense 2 by tone of voice and other cues). “I think we should
buy a VAX.”
“Mumble!” Common variant: mumble
frotz (see frotz; interestingly, one does
not say ‘mumble frobnitz’ even though ‘frotz’ is
short for ‘frobnitz’).

5. When used as a question (“Mumble?”) means “I
didn't understand you”.

6. Sometimes used in ‘public’ contexts on-line as a
placefiller for things one is barred from giving details about. For
example, a poster with pre-released hardware in his machine might say
“Yup, my machine now has an extra 16M of memory, thanks to the card
I'm testing for Mumbleco.”

7. A conversational wild card used to designate something one
doesn't want to bother spelling out, but which can be
glarked from context. Compare
blurgle.

8. [XEROX PARC] A colloquialism used to suggest that further
discussion would be fruitless.